use snake case for PHPUnit test methods

Author: othillo

.php_cs.dist

@@ -9,5 +9,6 @@ return PhpCsFixer\Config::create()
     ->setRules([
         '@Symfony' => true,
         'declare_strict_types' => true,
+        'php_unit_method_casing' => ['case' => 'snake_case'],
     ])
     ->setFinder($finder);